I don´t know how to explain it exactly, but the subjunctive is used to express an hypothetical situation.
In your example:
u otra que os parezca interesante = u otra que os pueda parecer interesante
Is like a second conditional : If I were you I would go to the party --> Si yo FUERA tú, iría a la fiesta.
In this case FUERA is a subjunctive.
I'm Sorry, but I can't give you a rule of thumb for the use of subjunctive.